Makes about 3.4 litres (6 UK pints)
2.75 kg (6 lb) fish bones from any firm-fleshed, white fish, such as halibut, sea bass, sole, monkfish or cod
3.4 litres (6 UK pints) cold water
225 g (8 oz) leeks
225 g (8 oz) (1 cup) chopped onions
450 g (1 lb) (2 cups) chopped carrots
100 g (4 oz) (½ cup) chopped shallots
8 sprigs of fresh parsley
4 sprigs of fresh thyme or 2 teaspoons dried thyme
2 bay leaves
5 garlic cloves, unpeeled and lightly crushed
2 teaspoons salt
1 tablespoon black peppercorns
1 Rinse the fish bones under cold running water until there is no sign of blood; the water should run clear. Put the bones in a very large pan, cover them with the cold water and bring to a simmer.
2 Meanwhile, trim the leeks and discard any yellow parts. Cut the leeks at the point where they begin to turn green and discard the green parts. Then split the white parts in half and rinse them well in cold running water until there is no trace of dirt. Coarsely chop the leeks.
3 Using a large, flat spoon, skim off the scum as it rises from the bones. Watch the heat, as the stock should never boil. Keep skimming until the stock looks clear; this can take 20–30 minutes. Do not stir or disturb the stock.
4 Now turn the heat down to a low simmer. Add the rest of the ingredients and simmer, uncovered, for 1 hour.
5 Remove the bones and other ingredients with a large, slotted spoon and strain the stock through several layers of dampened muslin (cheesecloth) or through a very fine-meshed strainer, then let it cool completely. It is now ready to be used or transferred to containers and frozen for future use.